Removing foreign material from the surface of work pieces is a critical element in the manufacturing of semiconductor devices. The presence of contaminants or foreign material can lead to critical failures or prematurely shortened life spans of these devices.
In manufacturing semiconductor devices, silicon work pieces known as "wafers" are used. Wafers typically have a flat, circular disk-like shape. Wafers are initially sliced from a silicon ingot and, thereafter, undergo multiple masking, etching, and dielectric and conductor deposition processes to create microelectronic structures and circuitry on the wafers. The surface of a wafer undergoing these processes typically must be polished or planarized between processing steps to ensure proper flatness, thus permitting use of photo lithographic processes for building additional dielectric and metallization layers on the wafer surface.
Chemical Mechanical Planarization ("CMP") machines have been developed to polish or planarize silicon wafer surfaces to the flat condition necessary for manufacture of integrated circuit components and the like. CMP processes and machines are known in the art and are described in several U.S. Patents. Examples include U.S. Pat. No. 4,805,348, issued in February 1989, to Arai, et al.; U.S. Pat. No. 4,811,522, issued in March 1989 to Gill; U.S. Pat. No. 5,099,614, issued in March, 1992 to Arai et al.; U.S. Pat. No. 5,329,732, issued in July, 1994 to Karlsrud et al.; U.S. Pat. No. 5,476,890, issued in December 1995 to Masayoshi et al.; U.S. Pat. Nos. 5,498,196 and 5,498,199, both issued in March, 1996 to Karlsrud et al.; and U.S. Pat. No. 5,558,568, issued in September 1996 to Talieh et al.
CMP processes typically require the introduction of a polishing slurry onto the surface of the wafer as it is mechanically polished on a polishing table. The slurries typically are water based and may contain fine abrasive particles and incorporate chemical cleaning compositions, such as silica and alumina. Consequently, CMP processing of the wafers may leave micro scratch marks and contaminants such as leftover slurry particles and unwanted metallic ions (sodium, potassium, iron, chromium, nickel, manganese, zinc, titanium, etc).
In a conventional method of cleaning work pieces, scrub brushes are used with deionized ("DI") water, ammonia, or various other chemical solutions. However, scrub cleaning the work piece alone may not remove implanted metallic ions or micro scratch marks. Additionally, the application of mechanical action in combination with some chemical solutions, such as hydrogen fluoride ("HF"), may result in introduction of sub microscopic scratches. Safety and waste disposal concerns may be further disadvantages of this cleaning method.
In another conventional method for cleaning work pieces, a static bath of chemical solution such as HF solution may be used. Work pieces are typically placed vertically into the HF solution to remove a layer of oxide from the surfaces of the work pieces. However, this method also has several short-comings. For example, the HF solution gradually degrades as the cleaning operation is repeated, thus making it difficult to control the amount of oxide layer that will be removed from the work pieces. Additionally, air bubbles adhering to the surfaces of the work pieces as they are placed into the HF solution may result in nonuniform etching of the work pieces. Further, the reaction of silicon oxide with HF results in the formation of silicon fluoride and water molecules. Both the silicon fluoride and water molecules tend to stay at the work piece surface/HF solution interface, which may result in nonuniform etching of the work pieces. More particularly, the water molecules remaining at the work piece surface/HF solution interface will dilute the concentration of the HF at the work piece surface. Therefore, a need exists for a method to remove contaminants and smooth scratches from the surfaces of work pieces which overcomes the various short-comings associated with existing conventional methods.